If you companion plant carrots with alliums (onion, spring onion, garlic), the carrots keep the onion fly away and the onions keep the carrot fly away. Marigolds are also a good protective plant to have around crops as they deter a lot of insects. And if you have a pot or two of bush basil near your doors, they keep flies out of the house.If you want to grow carrots then choose a variety that produces a shorter carrot. I don't think the very short ones are worth growing but there's plenty of stumpy ones. They do well for us in pots, the carrot fly seem to leave them alone as well.
One thing I have found is the modern peat free composts don't seem to hang on to the nutrients for long so pots need more feeding.
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